Ophthalmic microscopes, i.e. microscopes that are used for eye surgery, comprise typically two different kinds of illumination. A first illumination serves to illuminate a rather large field of view in the observed object, i.e. the eye to be operated. This illumination lightens the surroundings of the area, where the actual observation takes place. At the observed eye, the illuminated field of this type of illumination has a diameter between 60 mm and 80 mm. This illumination is referred to in the following as a main illumination. In eye surgery, the main illumination is primarily used to visualize outer eye structures like the cornea.
A second type of illumination makes use of the characteristic of the eye's retina to provide a reddish-orange reflection of light called the red reflex. The red reflex offers much higher contrasts than the main illumination and is mainly used for cataract surgery. The red reflex is generated by an illumination, which is coaxial or at least closely coaxial, e.g. within +/−5°, to the axis of an observer's pupil which looks through the illumination and observation system onto the observed eye. A known system for generating a red reflex is, for example, described in EP 0 661 020 B1. The field of illumination of the coaxial illumination is usually much smaller than the diameter of the main illumination, e.g. by a factor 2 to 5.
The image quality of the known illumination and observation systems, although having made large progress in the past, still leaves room for improvement.